Earth

No other occurence has ever had an impact on human society as enourmous as the destruction of Luna, the Earths first moon, a catastrophic event of biblic proportions.
The loss of the tidal effect, the state of random chaos the earths magnetic field was thrown into and the collapsing orbit almost led to the complete extinction of life on land. If forseen by our ancestors the event would surely have been described as armageddon. Within decades and only with unconditional support from outside was it possible to pull a big enough asteroid nearby into earthorbit, where it forms the second moon, Lillith, returning the planet to a somewhat stable condition. For more then a century Earth had lost any form of influence, be it political, economical or cultural. From the outdated calendar system due to the changed circumstances, to the languages and historic background, most colonies used this opportunity to become independant and a new order was wrapped over humanity.
Today Earth is mostly populated by humans on its surface, there are only a few plant and insect races left and the planets ecological cycle is mostly seabased. To this very day the planet still serves as the most efficient ground to cultivate biomass.
The difference in class within the human population is larger then ever, the several classes live strictly structured, with a large part of the population completely seperated from outside of the planet, just performing their tasks on the surface.
Several religions spreading through known space all consider Earth the holy birthplace of the human race, which has allowed Earth to claim a neutral position within the universe. Where colonies fight each other using embargos or warfare, Earth often provides the means to find diplomatic solutions. Its because of this that after the last major war the UCE was formed as an organisation around Earth.